Despite aggressive fluid resuscitation and topical antimicrobial therapy after burn trauma, sepsis frequently results from the loss of dermis; thus sepsis and resultant multiorgan failure are a major cause of death in the burn unit. Studies from the PI's lab and others' have shown that burn trauma and sepsis independently alter cardiocirculatory performance, and recent studies suggest that myocardial abnormalities after burn, trauma or sepsis are related to intracellular accumulation of calcium with subsequent cellular injury and dysfunction. Although this field has grown rapidly, much is still unknown about the cellular mechanisms underlying cardiac dysfunction after either trauma or sepsis. The PI's group have focused their attention on a clinically relevant model of burn injury complicated by sepsis (intratracheal administration of S. pneumoniae administered 24 hours postburn) and have shown progressive cardiocirculatory dysfunction in this two-hit model. Specific Aim 1a will determine if burn/sepsis exacerbates the increased [Ca2+] and [Na2+] shown to occur after burn alone and will determine the contribution of altered Na+/Ca2+ to cardiac contractile dysfunction. Specific aim 1b will determine the contribution of transient cellular acidosis and altered H+/Na+ exchange to increased [Na2+], and whether increased [Na+] in turn promotes Na+/Ca2+ exchange in [Ca2+] overload. Specific Aim 2 will determine the contribution of burn/ sepsis-mediated alterations in SR Ca2+ handling (SR Ca2+ efflux, Ca2+-ATPase activity, SERCA, and SR Ca content) to cellular Ca2+ and cardiac contractile deficits and determine the contribution of burn/sepsis induced myofilament Ca2+ insensitivity to cardiac contractile dysfunction. Studies in Specific Aim 3 will examine the role of PKC activation in intracellular Na+/Ca2+ accumulation and cardiac contractile dysfunction in burn sepsis. Studies in Specific Aim 4 will determine the contribution of increased [Ca2+] and reactive oxygen species to apoptosis in burn/sepsis and further determine the contribution of apoptosis to burn/sepsis-induced ionic derangements as well as cardiac contractile dysfunction. Only by understanding the cellular events involved in the postburn inflammatory cascade can adequate prevention and treatment modalities be designed to improve outcome.